Subscription television



Nov. 25, 1958 J. E. BRIDGES SUBSCRIPTION TELEVISION 4 Sheets-Sheet 1 Original Filed Deo.

HIS ATTORNEY.

Nov. 25, 1958 J. E. BRIDGES 2,862,049

SUBSCRIPTION TELEVISION Original Filed Dec. 15, 1952 4 Sheets-Sheet 2 FIG. 2

Reset Connection JACK E. BR|DGES INVENTOR.

HIS ATTORNEY.

Nov. 25, 1958 J. E. BRIDGES SUBSCRIPTION TELEVISION Original Filed Deo. 15, 1952 4 Sheets-Sheet 5 FIG?) xJEz O JACK E. BRIDGES INVENTOR.

HIS ATTORNEY.

J. E. BRIDGES SUBSCRIPTION TELEVISION Nov. 25, 1958 4 Sheets-Sheet 4 Original Filed Deo.

cozoccoo Emma EmEoguo corcmoamcocf JACK E. BRIDGES INVENTOR.

HIS ATTORNEY.

Lenaerts sunscnirrrors 1retevision:

Jack E. Bridges, Franklin Park, lll., assignor'to Zenith Radio Corporation, a corporation of Delaware Original application December 15, 1952, Serial No. 326,107. Divided and this application February 4, 1955, Serial No. 486,135

4 Claims. (Cl. 178--5.1)

This invention relates to means for producing an encoding signal for use in a subscription radio or television system or the like; more particularly, the invention pertains to a generator for developing a combination of code signal components individually having a predetermined identifying characteristic and collectively determining a code schedule in accordance with their distribution within the combination. This application is a division' of copending application Serial No. 326,107, filed December 15, 1952, and issued February 11, 1958 as Patent 2,823,252, in the name of .Tack E. Bridges, and assigned to the present assignee. l

The term encoding is used herein in its generic sense to encompass either coding at the transmitter or decoding at the receiver, since the encoding signal may be utilized in either the transmitter or receiver.

In copending applications Serial No. 281,418, led April 9, 1952, in the name of George V. Morris et al., and Serial No. 310,309, filed September 18, 1952, in the name of Alexander Ellett, both of which are assigned tothe present assignee, there is disclosed a generator for producing a combination or series of code signal components each having a predetermined identifying characteristic, such as frequency. These components represent a code schedule determined by their distribution withinV the combination, and are utilized to control theoperation of the encoding apparatus of a subscription television system in accordance with the code schedule. y

The generator shown in the aforementioned copendiug applications of Morris et al. and Ellett comprises a beamdeflection device which has a pair of deflection elements and a series of segmental anodes. A sweep system provides a saw-tooth shaped deflection signal to effect periodic and sequential scanning of the segmental anodes by the electron beam. Randomly occurring pulses` are applied to the input electrodes of the beam-deflection device, rendering the electron beamintermittently eilective. A series of generating units are connected to respective ones of the segmental anodes, and each is `responsive to the impingement of the electron beam on the associated anode to develop a code signal burst of a particular characteristic frequency and a predetermined duration. Thus, the generating units produce a combination or series of code signal components of different frequencies, appearing at times determined by the random keying of the electron beam. Instead of actuating the generators in a periodically repeating fashion, which would otherwise occur due to the periodic saw-tooth sweep, by randomly triggering the beam-deflection' tube on and off the order of actuation is occasionally interrupted.

While the code signal combinations produced in the Morris et al. and Ellett generator effect adequate picture scrambling with a relatively high degree of security against unauthorized appropriation, it may be desirable to further increase the complexity of the code signal.

To that end, the present invention improves both secrecy and scrambling by providing a generator wherein the-code generating units are selected in a completely random man- States Patent() Mce 2,862,049 Patented Nov.l 25,

ner without the limitation inherent in' previous arrangements introduced by the utilization of a periodically re curring saw-tooth shaped scanning signal.

Briefly, this is achieved inthe embodiment presently to be described by employing a beam-detlection Vtube having a series of target anodes individually coupled to'an assigned one of a series of signal generatorsin much Vthe same manner as in the Morris et al. and Ellett applica,- tions. However, instead of applying a periodically recurring saw-tooth shaped signal to the deflection elements, a noise signal is used having an instantaneous amplitude varying in random fashion. With `this arrangement,ffeach time the beam-deflection tubeis'keyed on, which is during each of a series of spaced predetermined timeA intervals, the deflection eld established by the noise signaldirects the electron beam to a randomly selected anode to effect actuation of a corresponding randomly selected generator,

It is, accordingly, an object of the present invention to provide an improved encoding signal generator of the/general type disclosed by Morris et al. and Ellett.

It is another object of the invention to provide a novel generator for developing en encoding signal which may be used for coding a program signal at a subscription `televsion transmitter and/or for decoding a coded program signal at a subscription television receiver. V

lt is still another-,object of the invention to provide a novel generator for developing combinations. of code signal components individually having va predetermined identifying characteristic and collectively determining .a code schedule in accordance with their distribution within each combination. i

The encoding signal generator of the presentl invention includes a code selection mechanism having a multiplicity of operating conditions and responsiveto a predetermined characteristic of an applied actuating signal for. actuation between' the operating conditions. The generator has means for producingV an actuating signal having the predetermined characteristic varying in a random manner, and also means for developing a series Vof signal lpulses collectively representing a series of spaced predetermined time intervals. Means is coupled to both 4of the aforementioned means and to the code selection mechanism for effectively applying the actuatingsignal to the mechanism only during each of the predetermined time intervals to render the mechanism responsive tothe characteristic during each such interval for establishing the mechanism in a randomly selected operating condition. A plurality of signal generators is provided for individually producing a signal having a predetermined identifying characteristic. Finally, the encoding signal .generator comprises means coupling the code selectionmechanism to the plurality of signal generators so that the generators are selectively operated inaccordance with the operating condition assumed by the code selection mechanism during each of the predetermined time intervals.

The features of-this invention Ywhich are believed vt0 be new are set forth with particularity in .the appended claims. The invention,together with.further objectsfand advantages thereof, may ,best berpunderstood,A however, by reference `to thefollowing description Whn taken in conjunction Withthe accompanying drawings, in which:

Figures 1 and 2 combined, with Figure 2 being` placed immediately belowY Figure4 l, constitute a .schematicdiagram of a subscription television transmitterincluding an encoding signal generator constructed in accordance with the invention; K

Figure 3 is a family of curvesuseful in explaining the operation. of the transmitter of Figures 1 and 2; and' Figure 44is a schematic diagram of a receiver for opand 2.

The transmitter of Figures 1 and' 2 includes a picture-` converting device which may be an iconoscope, image orthicon or other well-known type. The output terminals of device 10 are connected through a video amplifier 11 and an encoding apparatus or coder 12 to the input terminals of a mixer amplifier 13. Coder 12 may be similar to that disclosed and claimed in a copending application of Robert Adler, Serial No. 243,039, filed August 22, 1951, and issued August 7, 1956 as Patent 2,758,153, entitled Subscription Television System and assigned to the present assignee. It may comprise a beam-deflection tube having a pair of output circuits which may be selectively coupled into the video channel as the electron beam thereof is deflected from one to the other of two segmental anodes coupled to such output circuits. One of these circuits includes a time-delay network so that the timing of the video components relative to the synchronizing components of the radiated signal varies as the beam of the deflection tube is switched between its anodes. This switching effect is accomplished by means of a beamdeflection control or actuating signal applied to encoding apparatus 12, as explained hereinafter. Such intermittent variations in the relative timing of the video and synchronizing components effectively codes the television signal since conventional television receivers, not equipped with suitable decoding apparatus, depend upon an invariable time relation between the video and synchronizing components of a received signal to provide intelligible image reproduction.

Viewed from the standpoint of operating modes, coder 12 has two stable operating conditions each of which imposes a different operating mode on the transmitter. In the first operating condition, coder 12 extends the video channel from amplifier 11 to mixer 13 without introducing any material delay, and inV this condition the transmitter operation is conventional particularly in respect of the time relation between the video and synchronizing components of the radiated signal. In its second operating condition, coder 12 introduces a time delay in the video channel, and thetransrnitter then functions in an abnormal mode since the video and synchronizing components of the radiated signal have an abnormal time relation with respect to one another.

Mixer amplifier 13 is connected through a direct-current inserter 14 to a carrier-wave generator and modulator 15 which, in turn, is connected to an antenna 16, 17. The transmitter also includes a synchronizing-signal generator 19 which supplies lineand field-synchronizing components and associated pedestal components to mixer 13 over leads 20. Generator 19 further supplies fieldand line-drive pulses to a field-.sweep system 21 and to a linesweep system 22, respectively. The output terminals of sweep systems 21 and 22 are connected to the field-deflection elements 23 and line-deflection elements 24, respectively, associated with picture-converting device 111.

Generator 19 additionally supplies field-drive pulses to a mono-stable multivibrator 28 to produce an elongated pulse of a predetermined duration in response to each applied field-drive pulse. The output terminals of multivibrator 28 are connected to a mono-stable multivibrator 29 which is actuated from its normal operating condition to its abnormal condition in response to the trailing edge of each output pulse from multivibrator 28 to develop an output pulse of a predetermined time duration. The output signal from multivibrator29 is, iny

turn, applied as a gating signal to a normally-closed gate circuit 26.

Generator 19 also supplies line-drive pulses to a delay line 25 having output terminals connected to another input circuit of gate circuit 26 and further connected to an input circuit of another normally-closed gate circuit 32. The output terminals of gate circuit 26 are connected directly to a code burst generator 47, through a second delay line 27 to another mono-stable multivibrator 31, and over a conductor 34 to synchronizing-signal generator 19. The output terminals of multivibrator 3,1 are connected to the input terminals of gate circuit 32 to establish a gating signal therefor. The output signal of circuit 32 is also applied to synchronizing-signal generator 19 over conductor 34 and is supplied to a control grid of a code selection mechanism in the form of a beamdeflection device 38 to modulate the electron beam therein, energizing or turning on the beam for the duration of each applied signal pulse.

Beam-deflection device 38 includes a pair of deflection elements 36, 37 which are connected to the output terminals of a noise generator 35. This generator produces a signal having an amplitude characteristic that varies in random fashion within a suitable bandwidth and accordingly varies in amplitude from one operating instant to the next. This signal, as applied to deflection electrodes 36, 37, establishes an alternating beam-deflection field within code selection mechanism 38 having a peak-to-peak amplitude sutlicient to sweep the beam (if it is energized) back and forth across a family of anode segments 40a-40f at a rate corresponding to the rate of change of the output signal of generator 35. Because of the employment of the multiplicity of segmental anodes 48u-49j in conjunction with the pair of deflection elements 36, 37 which respond to an amplitude characteristic of an applied actuating or deflection signal from noise source 35 for directing the electron beam from one to another of the segmental anodes, code selection mechanism 38 is actuated between a corresponding multiplicity of operating conditions.

The load circuits for the several segmental anodes 40u-40]c are completed through control circuits of a series of additional code burst generators #l1-46, respectively. This coupling from the anode elements to the generators permits each generator to be turned on or energized by a current pulse resulting from the impingement of the beam Vin device 38 upon the associated anode segment. Each of the signal generators 41-47 includes a cycling or timing feature in the manner of a blocking oscillator or other mono-stable generator to determine the duration of the interval during which the generator is energized in order that the output obtained therefrom may have a selected duration, exceeding the current pulse delivered by its associated anode segment but less than the time separation of successive line-synchronizing pulses. Moreover, each of the generators 41-47 has a distinct, assigned operating frequency as indicated by the indicia f1-f7 to facilitate frequency selection or separation of the outputs from such generators. v

The respective areasV of the segmental anodes are preferably so chosen that each receives the same average current as the electron-beam is swept under the control of the signal applied to deflection elements 36, 37. The beam isl thus directed to each of the anodes for an equal proportion of each program interval and has a substantially equal probability of impinging on any one of the six anodes each time the beam is gated on under the control of unit 32.

It is convenient to utilize frequency as the identifying characteristic of the ouput signals of generators 41-47 although other characteristics such as pulse width and amplitude are also suitable.

The output terminals of signal generators 41-47 are connected to a pair of input terminals of mixer amplifier 13 over conductors 101 and, by means of a ground connection and conductor 102, to the primary winding of a transformer 58 which may be sectionalized, as illustrated. A series of secondary windings of transformer 58 which constitute the inductive portions of a corresponding series of frequency-selective tuned circuits 51-57, each such circuit being resonantat a particular one of the frequencies )c1-f7, is provided to separate the code signal components from one another. The frequency-selective circuits,.with the exception of circuit V57, are connected through diode rectifiers6166 to a transposition mecha-Y nism 70 While frequency-selective circuit 57 is connected;

through a diode vrectitier 67 to a reset connection 79. The transposition mechanism 70 includes a series of switching devices 71-76, one for each of the selector circuits 51 to 56, respectively. Each such switching device comprises a first switch blade connected to the anode of the diode in circuit with its selector and adjustable to engage either of two contacts. Each of these contacts, in turn, is connected to second and third switch blades individually adjustable to engage either one of a further pair of terminals so that the circuit may be extended from the input terminal of the switching device to any one of four output terminals in accordance with the adjustment of the first, second and third switch blades. The second and third blades of each switching device are mechanically interconnected, as represented by the broken construction line, for unicontrolled action in respect of their contact pairs. Corresponding output terminals of the switching devices are interconnected by conductors 77a-77d. Conductors 77a-'77d extend the circuits from the active output terminals of the switching devices to resistance-capacitance diode load circuits 81, 82, or 83 or, alternatively, to a ground connection 30.

The described circuitry of transposition mechanism 70 permits selective control of a control mechanism or multistable actuating device 103 provided for supplying a beamdeflection signal to coder 12 to effect actuation thereof and coding. As shown and as will be described presently, the actuating device has two stable operating conditions resulting from the use of a pair of electron-discharge devices 77 and 78 cross-coupled, one to the other, to be rendered conductive in alternation. If desired, a ring circuit may be used in the actuating device to provide a larger number of stable operating conditions and increase the flexibility as well as the capability of the coding technique. The use of a multi-stable actuator having a large number of stable operating conditions further reduces the number of frequency channels required for coding. Considering now more particularly the form of actuator represented, it comprises a pair of electron-discharge devices 77 and 78, the anode of device 77 being cross-coupled to the control electrode 105 of device 78 through a resistor 97 and the anode of device 78 being cross-coupled to the control electrode 104 of device 77 through a resistor 93. The anodes of devices 77 and 78 are connected through resistors 96 and 99, respectively, to a source of positive unidirectional operating potential 95, and the cathodes of the devices are connected in common through the parallel combination of a resistor 94 and a capacitor 93 to a ground connection.

The control mechanism or actuator has three input circuits for individually controlling the conductive condition of an assigned one of theV discharge paths to determine the operating condition of the actuating device. One input circuit, coupled to the grid 104 and cathode of tube 77 to control'the conductivity thereof, comprises a diode 84 connected between the high-potential terminal of network 82 and a resistor 91. A second input circuit for controlling the conductivity of tube 7S comprises a diode 87 and a resistor 92 coupled in similar fashion in respect of the high-potential terminal of network 83 and grid 105 of tube 78. The third input circuit extends from lthe highpotential terminal of network S1 through one diode 85 to grid 104 of tube 77 and, alternatively, through another diode 86 to grid 105 of tube 78. The anode of tube 7S is connected to coder 12 over conductors 100 to provide an actuating or deflection-control signal therefor having amplitude variations representing a coding schedule and determined by variations in the operating condition of actuator 163.

In order to restore actuating device 103 to a reference operating condition at predetermined times, reset connection 79 permanently connects frequency-selector 57 to the first-described input circuit of device 103 by way of conductor 77b.

In considering the operation of the described transmitter, the techniqueof coding will be disregarded initially. Picture-converting device 16 produces video-frequency components representing the program information to be televised and these components, after amplification in amplier 11, are supplied through encoding apparatus or coder 12 to mixer amplilier 13. The mixer also receives the usual lineand field-synchronizing and blanking pulses from generator 19 so thata composite television signal is developed therein. That signal is adjusted as to background level in direct-current inserter 14 and is amplitude modulated on a picture carrier in unit 15. The modu- .lated video carrier is supplied vto an antenna 16, 17 for transmission to subscriber receivers. It will, of course, be understood that in the generation of the Video-frequency components sweep systems 21 and 22 are synchronized by the fieldand line-drive pulses applied thereto by generator 19. As in any television broadcast, the' accompanying audio information is modulated on a sound carrier and concurrently radiated. However, the sound system may be entirely conventional and since it constitutes no part of the instant invention, it has not been illustrated in order to avoid unnecessarily encumbering the drawing.

It is necessary in any commercial subscription system to code the video signal, and preferably the sound signal as well, to prevent pirating or unauthorized use of the program material. Briefly, coding of the video portion of the broadcast is accomplished by coder 12 under the influence of a deection-control signal which switches the beam thereof back and forth between its two segmental anodes in accordance with a coding schedule represented by amplitude variations of that signal. As previously explained, this actuation of the coder varies the operating mode of the transmitter, modies the time relation of the video and synchronizing components of the radiated signal, and achieves coding., Consideration will now be given to the particular manner in which the encoding signal is developed in accordance with the invention and the manner in which it is utilized to codeV the telecast.

leriodically recurring line-drive pulses, shown in curve A of Figure 3, are supplied from generator 19 to delay line 25 to establish the pulses of curve B, This line is terminate-d in its characteristic impedance and exhibits a delay exceeding the duration of the line-drive pulses but substantially less than the time separation of such pulses. Simultaneously with the application of line-drive pulses to delay line 25, periodically recurring field-drive pulses, shown in curve C, are applied to multivibrator 28. The leading edge of an applied field-drive pulse actuates the vmultivibrator from its normal operating condition to an abnormal operating condition and the multivibrator automatically returns to its normal condition after a selected time interval determined by its internal cycling circuits to produce the pulse of curve D. The parameters of the multivibrator are so chosen that the trailing edge of this pulse occurs during the field-retrace time of the system, at a point following the equalizing pulses which succeed the serrated iield pulse in present-day practice.`

This output signal is applied to mono-stable multivibrator 29 whichV responds to the trailing edge thereof and produces a gating pulse, shown in curve E. The parameters of multivibrator 29 are so chosen that this pulse overlaps, in point of time, one pulse from delay line 25. Gate circuit 26 receives the gating pulse as well as delayed line-drive pulses from delay line 25 and responds to their coincident eiect to translate a pulse (curve F) to generator 47. This generator is energized by the applied pulse and develops a burst of signal of frequency f7 having a time duration exceeding the duration of the actuating pulse but less than the time separation of successive'line-synchronizing pulses. This signal burst of frequency f7 produced at the output terminals of unit 47 is for reset purposes and is shown in curve I. The utility of this reset burst will be shown hereinafter.

The output signal from gate circuit 26 (curve F) is also delayed in delay line 27 which is terminated in its characteristic impedance and which exhibits such a delay that its output pulse, shown in curve G, follows the trailing edge of the pulse of curve F. The delayed output pulse is applied to mono-stable multivibrator 31, producing a gating pulse, shown in curve H for gate circuit 32. The parameters of multivibrator 31 `are so chosen that its output pulse (curve H) overlaps, in point of time, the number of delayed line-drive pulses (curve B) to 'be employe-d in coding-six for the case in question. Delayed line-drive pulses are continuously supplied from delay line 25 to gate circuit 32 and those which occur within the duration of the gating pulse are translated to code selection mechanism or beam-deflection device 38. The translated pulses, shown in curve I, represent a series of spaced predetermined time intervals and intensity modulate the beam, turning the beam on so to speak for the duration of each such pulse. At the same time, the variable amplitude sweep signal impressed on deflection elements 36, 37 by noise generator 3S creates a deflection field varying at a random rate to scan the beam back and forth across segmental anodes 40u-401V Each time a pulse'of curve I is applied to the control'electrode, a pulse of current flows in the circuit of one of the segmental anodes to turn on the one yof generators 41-46 that is coupled thereto. The triggering effect of the pulses of curve I eectively causes application of the actuating or deflection signal to code selection mechanism 38 only during each of the spaced predetermined time intervals to render the mechanism responsive to the signal occurring during each such interval. In the present illustration, for example, it will be assumed that when the first pulse of curve I occurs, the beam is directed to anode 40o and thus generator 43 produces a burst of signal of frequency f3. It will further be assumed that as the succeeding pulses of curve I occur, generators 42, 46, 41, 44, and 42, are turned on in the recited order, producing corresponding bursts of signal of frequencies f2, f6, f1, f4, and f2, as shown in curve I. A combination of code signal components of various frequencies is thus established, the components being randomly-sequenced and randomly-appearing within their combination.

These code signal components are impressed on the primary winding of transformer S 'and are selected by means of frequency-selectors 51-57. In other wo-rds, the first burst of signal of frequency fr, is segregated by selector 57, the second burst of signal of frequency f3 is segregated by selector 53, the third burst of signal of frequency f2 is chosen by selector 52, and so on. Assuming that transposition mechanism 70 is adjusted as illustrated, selector 51 is coupled through diode 61 and switching element 71 to load circuit 03; selector 52 is coupled through diode 62 and switching element 72 to load circuit 81; selector 53 is coupled to load circuit 83; selector 54 is coupled to ground; selector 55 is coupled to load circuit S2 and selector 56 is coupled to load circuit 81. Thus, the reset pulse shown in curve K is developed in network 82 in response to the burst of signal frequency f7; the pulses of curve L are developed in network 81 in response to the two bursts of signal frequency f2 and the single burst of signal frequency f6; and the pulses shown in curve M are developed in network 83 in response to the burst of signal frequency f3 and the burst of signal frequency f1. It will be noted that the burst of signal frequency f4 is channeled directly to the ground and develops no signal potential in the load circuits.

It is thus seen that the transposition mechanism receives a particular combination of code signal cornponcnts (curve I) and transposes that combination into a different effective combination (curves K, L and M) determined by the adjustment of its switch elements 71 to 76 which direct the pulses of the first combination in respect of the input circuits of the control mechanism or bi-stable actuating device 103. In considering the V8 v transposition effected by mechanism 70 it will be manifest that the distribution of the coding pulses in respect of the input circuits of actuating device 103 is particulari ly significant in determining the nal coding pattern. The specific setting of transposition mechanism 70 may be changed at will although it is convenient to adjust the' mechanism at the start of a program and maintain it throughout the program. The switch setting informa` tion is disseminated only to subscriber receivers and a suitable charge may, of course, be assessed for such information.

Consider that in the first or reference operating condition of. actuator 103, tube 77 is non-conductive and tube 78 is highly conductive; further consider that in the second or alternative operating condition, tube 77 is highly conductive and tube 78 is non-conductive.

In describing the effect of the transposed signal components upon actuator 103, it will be assumed initially that the actuator is in its second operating condition at the start of the mode-determining interval. The reset pulse of curve K which is received first is applied to control electrode 104 of device 77. The reset pulse biases device 77 to cut-off and the cross-coupling causes device 78 to be conductive, thus establishing the reference Operating condition in the actuator. If actuating device 103 is in its reference condition at that time the reset pulse has no effect at all. In this manner, the actuator is certain to be in its reference condition at the beginning of each combination of coding signal pulses; the period for the combination is called a mode-determining interval inasmuch as the combination determines the particular mode of operation of the system for an ensuing operating interval, i. e., the succeeding field-trace interval in the particular illustration.

The next pulse, which is the rst component of curve M, is appliedV from network S3 to control electrode 105 and 4causes device '7,8 to be driven bey-ond cut-off which, in turn, renders device 77 conductive. The actuator` is thus triggered to its second operating condition. The next succeeding pulse of the coding combination which is the first pulse of curve L is impressed simultaneously on both control electrodes 104 and 105 from network S1. Device 7S being already non-conductive is not effected by the negative signal on its control electrode 105, whereas device '77 being in its conductive state is rendered non-conductive and device 78 then becomes conductive. The next succeeding pulse of the coding combination, which is the second component of curve L, is also applied from network 81 to control electrodes 104 and 105. The negative signal applied to control electrode 104 has no effect on device 77 whereas the signal impressed on control electrode 105 biases device 73 beyond cut-off which renders device 77 conductive. The actuator thus assumes its second operating condition. The next pulse of the transposed combination, which is the second component of the curve M, is applied from network 83 to control electrode 105 but has no effect since device 7S is already nonconductive. The next pulse of the original combination, a burst of signal of frequency f4, is applied to ground through switch element 74 and does not reach actuator 103. The final pulse of the transposed combination is the last component of curve L and is applied from network 81 to control electrodes 104 and 105. It triggers the circuit to its first operating condition.

The resulting signal obtained from device 78 of bistable actuating device 103 (curve N) is applied to coder 12 over co-nductors 100 as a deflection-control signal. The amplitude excursions of this signal shift the beam of coder 12, and the amplitude level of the signal at the conclusion of the response of actuator 103 to the transposed code combination determines the operating mode of the system until the next succeeding mode-determining interval at which time the aforedescribed modedetermining process is repeated. In view of the random to such lsubscriber receivers.

9,. manner in which the frequency components may appear in the original combination (curve I), it is apparent that the Inode-determining process causes the operating mode of the system to change from time to time in accordance with a random coding schedule. As a consequence, the transmission is coded.

in order that subscriber receivers may utilize the coded transmission, it is necessary that the combination of code signal components developed by beam-deflection device 33 and its associated circuitry be made known To that end, the code signal combination (curve I) ,is applied to mixer amplifier 13 at the same time it is delivered to transposer 70 to be combined with the composite video signal for transmission to subscriber receivers. The bursts of various signal frequencies, which constitute the code signal, occur between the line-drive pulses superimposed on the vertical-blanking pulse, and therefore it is desirable that the amplitude level of the blanking pulse be modified to effect an inward modulation of the blanking pulse by the coding signal components. To that end, the pulses shown in curves F and i are supplied to synchronizing-signal generator 19 over conductor 34 to produce suitable modulating pulses which, in turn, are supplied to mixer amplifier 13 over conductors 20 to downward modulate the vertical blanking pulse at the appropriate times. inasmuch as the time duration of the modulating pulses should equal the duration of the signal bursts (curve J) and will therefore exceed the duration of the actuating pulses shown in curves I and F, signal generator 19 may include a timing device, such as a mono-stable multivibrator, to develop such modulating pulses of selected time duration in response to the actuating pulses. The effect of the application of these modulating pulses and the code signal components to the mixer amplifier' 13 is readily apparent by observing the wave form of the radiated compositeV video signal shown in curve O.

It should be mentioned at this time that in the particular illustration the code signal componentsl are produced during a portion of the vertical-retrace interval so that mode changes will be effected between field-trace intervals. However, it should be understood that the Vcode signal may Ibe developed and utilized at o-ther times, for example during line-retrace intervals, if so desired.

The receiver of Figure 4, which may utilize the encoding signal and the telecast originating at the transmitter of Figures l and 2, comprises a radio-frequency amplifier 1111 having input terminals connected to an antenna circuit 111, 112 and output terminals connected to a first detector 113, the output terminals of the detector being connected to an intermediate-frequency amplifier 111. The output terminals of the intermediate-frequency amplifier are connected through a second detector 115 to a video amplifier 116 which, in turn, is coupled through an encoding apparatus or decoder 117 to the input electrodes 113 of a cathode-ray image-reproducing device 121. Decoder 117 may be similar to coder 12 at the transmitter except that it is controlled to operate in a complementary fashion in order effectively to cornpensate for the variations in the timing of the received television signal.

Second detector 115 is also coupled through a synchronizing-signal separator 122 to a field-sweep system 123 and a line-sweep system 124. The output terminals of sweep systems 123 and 124 are connectedlrespectively to field-deflection elements 120 and line-defiection elements 119, associated with reproducing device 121.

Field-drive pulses derived from synchronizing-signaly separator 122 are supplied to a mono-stable multivibrator 125 having output terminals connected to a normally-closed gated amplifier 126. The output terminals of second detector 115 are also connected to gated amplifier 126 to supply the composite video signal thereto,

and the output circuit ofrthisamplifier is completedk through a sectionalized primary windingof a transformer 138 to a source of unidirectional operating potential 127. A series of secondary windings of the transformer constitute the inductive portions of a series of frequencyselective tuned circuits 131-137, individually resonant at a particular one of the seven frequencies employed in coding. Selectors 131 to 136 are connected via associated diode rectifiers 141-146 to a series of switching elements 151-156 while selector 137 is directly connected via a reset connection 182 toV a parallel resistance-capacitance load circuit 161. Switching elements 151-156 constitute a transposition mechanism 158, similar to mechanism 70 of the transmitter, provided to connect any one of the selectors 131-136 to any one of three parallel resistancecapacitance load circuits 160, 161, 162 or to ground.

Load circuit 160 is connected via conductor 184 and a pair of isolating diodes 165, 164 to the control electrodes 178 and 179 of a pair of electron-discharge devices 171 and 172, respectively, of an actuator 183. These control electrodes are connected to ground throughA resistors 167 and 168. respectively. Load circuits 161 Aand 162 are connected 'to control electrodes 178, 179 of devices 171, 172, respectively, via conductors 135, 180 and isolating diodes 163 and 166. The anode of device 171 is crosscoupled to the control electrode 179 of device 172 through a resistor 175 and the anode of device 172 is crosscoupled to the control electrode 178 of device 171 through a resistor 176. The anodes of devices 171, 172 are also connected through resistors 173 and 174, respectively, to a source of unidirectional operating potential 177 and the cathodes of the devices are connected in common through the parallel combination of a resistor 170 and a capacitor 169 to a ground connection. The anode of device 172 is connected to decoder 117 over conductors 181 to provide an actuating or deflection-control signal therefor. The decoding arrangement shown in Figure 4, comprising the frequency-selective circuits, the transposition mechanism and the bi-stable actuating circuit is identical to the corresponding arrangement shown in Figure 2.

In operation, the coded television signal from the transmitter of Figures l and 2 is intercepted by antenna circuit 111, 112, amplied by radio-frequency amplifier and heterodyned to the selected intermediate-frequency of the receiver in first detector 113. The resulting intermediatefrequency signal is amplifiedin intermediate-frequency amplifier 114 and detected in second detector 115 to produce a composite video signal. This latter signal is amplified in video amplifier 116 and impressed on the input electrodes 118 of image reproducing device 121 through decoder 117 to control the intensity of the cathode-ray beam of the device in well known manner.

The synchronizing components are separated in separator 122, the field-synchronizing components being utilized to synchronize sweep system 123 and, hence, the field scansion of image-reproducing device 121, Whereas the line-synchronizing components are utilized to synchronize sweep system 124 and, therefore, the line scansion of device 121. Of course, the sound modulated carrier received along with the video carrier is translated in the usual way through an audio system which has been omitted lfrom the drawings for purposes of simplicity.

Y Field-drive pulses `from separator 122 are supplied to mono-stable multivibrator to produce a gating pulse shown in curve P for normally-closed gated amplifier 126. The parameters of the multivibrator are so chosen as to overlap, in point of time, that portion of the field-retrace interval of the composite video signal (curve O) which includes the reset pulse and the other encoding signal pulses. The composite video signal is continuously applied to the input circuit of amplifier 126 but only the information contained during the interval of the gating pulse (curve P) is translated to the primary winding of transformer 138. Amplifier 126 is thus open during the times the signal bursts of various frequencies, representing the combination of code signal pulses, are received and consequently such bursts are separated out by the selector circuits 131-137 in the same manner as in the transmitter. When the various switching elements 151- 156 of transposition mechanism 158 are adjusted to the same setting as transposition mechanism 70 at the transmitter, the input circuits of bi-stable actuating device 183 receive the identical pulses received by the corresponding input circuits of bi-stable actuating device 103 of the transmitter to produce an actuating or deflection-control signal for decoder 117 identical in wave form to curve N. Decoder 117 therefore operates in time coincidence with coder 12 at the transmitter so that the signal applied to electrodes 118 of image-reproducing device 121 is suitably compensated to effect proper image intelligibility.

By way of summary, beam-deection tube 38 and its associated control, deflection and target electrodes, constitute a code selection mechanism having a multiplicity of operating conditions and which responds to a predetermined characteristic (for example, amplitude) of an applied actuating signal for actuation between the operating conditions. Noise generator 35 produces an actuating or deflection signal having such a predetermined characteristic varying in a random manner. Gate circuit 32 and its actuating circuitry, and the connections from noise generator 35 and gate circuit 32 to beam-deflection tube 38 constitute means for eifectively applying the actuating signal to the code selection mechanism during each of a series of spaced predetermined time intervals (represented by the pulses of curve I) to render the mechanism responsive to the amplitude characteristic of that actuating signal during each such interval, thereby to establish the mechanism in a randomly selected operating condition. Generators 41-46 provide a plurality of signal generators for individually producing a signal having a predetermined identifying characteristic, namely frequency. Finally, the coupling circuitry between segmental anodes 40a-40f and generators i1-46 constitute means coupling code selection mechanism 38 to the plurality o-f signal generators so that the generators are selectively operated in accordance with the operating condition assumed by the code selection mechanism during each of the aforesaid predetermined timeintervals.

The invention provides, therefore, a novel encoding signal generator for developing Acombinations of code signal components individually having a predetermined identifying characteristic and collectively determining a code schedule in accordance with their order within eac'h combination.

Certain features disclosed in the present application are also described and claimed in copending application Serial No. 700,854, led December 5, 1957, in the name of Myron G. Pawley et al., constituting a divisional application of copending application Serial No. 230,618, led June 8, 1951, and issued December l0, 1957 as Patent 2,816,156; and copending application Serial No. 700,855, led December 5, 1957 in the name of Jacob M. Sacks, consituting a continuation of copending application Serial No. 259,169, tiled November 30, 1951, all of which are assigned to the present assignee.

While a particular embodiment of the invention has een shown and described, modifications may be made, and it is intended in the appended claims to cover all such modifications as may fall within the true spirit and scope of the invention.

I claim:

1. An encoding signal generator comprising: a code selection mechanism having a'multiplicity of operating conditions and responsive to a predetermined characteristie of an applied actuating signal for actuation between said operating conditions; means for producing an actuating signal having said predetermined characteristic varying in a random manner; means for developing a series of signal pulses collectively representing a series of spaced predetermined time intervals; means coupled to both of said aforementioned means and to said code selection mechanism for effectively applying said actuating signal to said mechanism only during each of said predetermined time intervals to render said mechanism responsive to said characteristic during each such interval for establishingy said mechanism in a randomly selected operating condition; a plurality of signal generators for individually producing a signal having a predetermined identifying characteristic; and means coupling said mechanism to said plurality of signal generators so that said generators are selectively operated in accordance with the operating condition assumed by said code selection mechanism during each of said predetermined time intervals.

2. In a subscription television transmitter including a source of periodically recurring line-drive pulses, an encoding signal generator comprising: a code selection mechanism having a multiplicity of operating conditions and responsive to a predetermined characteristic of an applied actuating signal for actuation between said operating conditions; means for producing an actuating signal having said predetermined characteristic varying in a random manner; means coupled to said source for delaying said line-drive pulses to develop a series of pulses interlaced with said line-drive pulses; means coupled to said delaying means, said code selection mechanism and said actuating signal producing means for effectively applying said actuating signal to said mechanism only during each of the delayed line-drive pulses to render said mechanism responsive to said characteristic during each such delayed line-drive pulse for establishing said mechanism in a randomly selected operating condition; a plurality or signal generators for individually producing a signal having a predetermined identifying characteristic; and means coupling said mechanism to said plurality of signal generators so that said generators are selectively operated in accordance With the operating condition assumed by said code selection mechanism during each of the delayed line-drive pulses.

3. An encoding signal generator comprising: a code selection mechanism including a beam-deflection device having a multiplicity of segmental anodes, means for developing an electron beam within said bcam-deection device, and a pair of deection elements responsive to an amplitude Vcharacteristic of an applied deflection signal for directing said electron beam from one to another of said segmental anodes to eiect actuation of said code selection mechanism between a corresponding multiplicity of operating conditions; means for producing a deflection signal having an instantaneous amplitude varying in a random manner; means for effectively applying said deection signal to said deflection elements during each of a series of spaced predetermined time intervals to direct said electron beam to a randomly selected segmental anode during each such interval for establishing said mechanism in a correspondingly randomly selected operating condition; a plurality of signal generators for individually producing a signal having a predetermined identifying characteristic; and means coupling each of said segmental anodes to an assigned one of said generators so that said generators are selectively operated in accordance with the operating condition assumed by said code selection mechanism during each of said predetermined time intervals.

4. An encoding signal generator comprising: a code selection mechanism including a beam-deflection device having a control electrode, a multiplicity of segmental anodes, means for developing an electron beam within said beam-deflection device, and a pair of deflection elements responsive to an amplitude characteristic of an applied deflection signal for directing said electron beam from one to another of said segmental anodes to effect actuation of said code selection mechanism between a corresponding multiplicity of operating conditions; a noise generator for producing a deflection signal having an instantaneous amplitude varying in a random manner;

14 each of said segmental anodes to an assigned one of said generators so that said generators are selectively operated in accordance With the operating condition assumed by said code selection mechanism during each of said pre- 5 determined time intervals.

References Cited in the lile of this patent UNITED STATES PATENTS 10 2,414,101 Hogan et al. Jan. 4, 1947 2,472,774 Mayle June 7, 1949 2,656,407 Herrick et al. Oct. 20, 19,53 

